body{
    background-image: url(../images/index.jpg);
    background-attachment: fixed;/*固定背景*/
    background-repeat: no-repeat;
    background-size: cover;
    background-position: center center;
}

h2 {
    width: 350px;
    height: 260px;
    margin: 0px auto;
    margin-top: 200px;
    padding-top: 10px;
    padding-bottom: 10px;
    /*background: rgba(0,0,0,0.4);*/
    text-align: center;
    color: #fff;
}